In general, a wireless electrical energy transmission device includes an electrical energy transmitting end and an electrical energy receiving end to transmit energy by means of electromagnetic induction or magnetic resonance. The electrical energy transmitting end includes an inverter and a transmitting coil. The invertor receives DC voltage to generate AC voltage. The transmitting coil receives an alternating field with a frequency ω0 generated by AC voltage. The receiving coil of the electrical energy receiving end is coupled with the alternating magnetic field to generate alternating voltage Vsin (ω0) with the frequency ω0. Generally, the lower the frequency of the alternating field is, the shorter the distance of the electrical energy transmission is. Therefore, in order to increase the distance of the wireless electrical energy transmission, the frequency of the alternating field must be increased. According to wireless charging standards, such as Qi and PMA wireless charging standards, in an electromagnetic induction wireless electrical energy transmission system, the frequency of the alternating magnetic field is in the range of 100 kHz-500 kHz and the distance of the electrical energy transmission distance is usually one centimeter or less; according to A4WP wireless charging standards, in a magnetic resonance wireless electrical energy transmission system, if the frequency of the alternating magnetic field is 6.78 MHz, the distance of the corresponding electrical energy transmission is up to several centimeters.
In order to increase the distance of transmission, it usually uses magnetic resonance wireless electrical energy transmission and generates an alternating magnetic field with the frequency of 6.78 MHz. The corresponding switching component of an inverter works at the frequency of 6.78 MHz. When the switching component works at the frequency of 6.78 MHz, the switching component will have a large switching loss. This may shorten the service life of the switching component greatly. In order to reduce the loss, it needs the soft-switching technology (ZVS) to lower the loss of the switching component.
Furthermore, an inverter circuit in a half-bridge or full-bridge bridge configuration needs two or more switching components to work together. But at such a high operating frequency of 6.78 MHz, it is difficult to precisely control the dead-time between a plurality of switching devices. The switching devices may be wrongly connected or disconnected at the same time, which reduces the safety and reliability of the circuit.